Scanning probe microscopes (SPMs) are instruments that provide high resolution information about surface contours. Vertical movement of a sensing probe, in response to a raster scanning procedure of the sensing probe across a target surface, is used for determining the target surface contour. Implementations of SPM devices include implementations based on the interaction of attractive forces including atomic, electrical potential, magnetic, capacitive, or chemical potential to maintain a constant probe to target surface gap, or distance. One common use of these devices is imaging. Some types of SPMs have the capability of imaging individual atoms.
In addition to imaging surface contours, SPMs can be used to measure a variety of physical or chemical properties with detail over the range from a few Angstroms to hundreds of microns. For these applications, SPMs can provide lateral and vertical resolution that is not obtainable from any other type of device. Examples of applications include imaging or measuring the contour properties of transistors, silicon chips, disk surface, crystals, cells, or the like.
In order to provide for high resolution information about surface contours, variables for the SPM include the effective size of the scanning probe, the positioning of the scanning probe above the target surface, and the precision of the scanning device itself.
The positioning of the scanning probe above the target surface is to be at a distance of one or two atoms, or an order of magnitude of tens of Angstroms. Further, a non-contact method of positioning is desirable and is the subject of the copending application Ser. No. 07/897,646.
Traditionally, scanning probe microscopes have a carriage which can be displaced in x and y directions by means of a piezoelectric actuator, with facilities for fine adjustment. While the arrangement theoretically permits minute displacements of the carriage, it is more difficult to operate the smaller the desired displacement is. This is due to a certain unavoidable backlash in the mechanism and because of the natural friction of the resting stage, which is only overcome with a sudden and mostly exaggerated movement. In addition, some piezoelectric elements have some undesirable properties such as hysteresis, creep, and nonlinear motion.
Further, during the scanning procedure, it is desirable to move the carriage independently in a single plane. More specifically, in measuring surface microtopography, in order to survey a surface area accurately, the carriage used to move the scanning tip across the target surface must offer flat motion (i.e. move in a single plane). Flatness is key to large area angstrom level vertical measurements, inasmuch as any vertical deviation of the carriage cannot be separated from either the measurement of the surface contour and therefore contributing to the vertical measurement, or from a component contributing to a noise level. In the first instance, an "out-of flat" carriage motion is one that leads to an anomaly in the apparent surface contour thereby degrading the accuracy of the scanning procedure and integrity of the scan result. In the second instance, the "out-of flat" carriage motion offers a significant component to the noise level of the resulting scan.
Flexure devices or hinges permit motion or displacement in a member made of normally non-flexible material. Cut-outs or recesses within a flexure assembly may be separated by web-like sections that are sufficiently thin to provide a desired flexure capability. Such an embodiment is shown, for example, in U.S. Pat. No. 4,559,717. However, the embodiment is one that offers an in plane flexure that offers motion in one direction only, thereby making the device not suitable for scanning.
Further, thermal creep becomes critical when making measurements at the tip to target surface gaps of attractive force measurements. Thermal creep refers to the relative motion of the sample in relation to the probe tip caused by a change in temperature. It is a time dependent function that need not be linear or monotonic, and therefore cannot be fully corrected by use of postprocessing schemes. Thermal creep is a function of many parameters, including: thermal expansion coefficients, magnitude and application of thermal gradient, shape of materials, and thermal mass of materials. Any one, or a combination, of the above parameters can effect the integrity of the scanning procedure as the tip to target surface gap varies due to thermal creep, thereby degrading the accuracy of the resulting scan.
In view of the fact that the resolution of the new microscope developments and the requirements in electronic circuit manufacturing have increased over several orders of magnitude, it has become necessary to design new positioning devices which avoid the disadvantages of the prior art.